1. Field of the Invention
The present invention relates generally to the field of electromagnetic switches and more particularly to a new and improved arrangement for locking a reed capsule within a magnetic latching reed switch assembly.
2. Description of the Prior Art
In modern telephone systems the reed switch has found wide acceptance as a crosspoint in switching matrices. One recently developed form of this type of switch is disclosed in U.S. Pat. No. 3,783,421, granted Jan. 1, 1974, to Sigitas Miknaitis. The reed capsules are housed in an axially extending internal compartment in a bobbin which has a base forming flange at one end. A plurality of coil terminals and associated pins are disposed about the base for entering into contact with apertures arranged in a corresponding pattern on a wiring card.
A distinct feature of the above mentioned switch was the method used for locking the reed capsules within the bobbin. The upper end of the bobbin is provided with slots which are adapted to receive the transverse portion of an L-shaped return strap. The return strap is attached by welding the transverse portion to the upper reed capsule lead and inserting it within the slots, it is finally locked into position by a means of a under cut tab found adjacent to the slot.
Initially, the switches were designed with 0.022 diameter nickel silver wire return straps. The original wire had sufficient ductility to enter into the under cut tab without much destruction of the molded plastic corner or damage to the capsule seals. Accordingly, sufficient retention forces were provided to hold capsules in the bobbin.
To satisfy field performance requirements it was necessary to institute a change to magnetic return straps of 0.026 diameter steel wire. To accommodate the heavier return straps the bobbin crown was modified according to the original under cut tab method. Experiments with bobbins molded to accept the heavy return straps, even after several attempted changes, were unsatisfactory. Numerous tests indicated the existance of two adverse conditions. Assemblies with sufficient retention forces required excessive insertion forces to snap into the under cut. These assemblies contained a large percentage of capsules with cracked seals. Conversely, assemblies with acceptable insertion forces produced many capsules that became unlatched during handling and electrical inspection. The main difficulty was traced to relatively stiff steel return straps that deformed most of the plastic corner intended to retain the capsule in the device.
To achieve the best balance between low insertion force and high retention the flexible tab concept was introduced.
Accordingly, it is the object of the present invention to provide a new and improved arrangement for locking a reed capsule within a magnetic latching reed switch assembly.